In the field of modern communications, it is well known to provide various communication services to a user via a packet data network. Consider the example of a computer terminal accessing a web page hosted on a remote server. When a user of the computer terminal wishes to access the web page, a request is sent across the packet data network to the remote server which responds by sending packet data back to the computer terminal corresponding to the requested web page. Other examples include “real-time” services such as voice communications. Voice communications may be undertaken for example by a communications terminal using an internet protocol (VoIP) application. The terminal is typically connected to the packet data network and voice data is communicated to and from the terminal by the transmission of packets across the network. Often, a VoIP server will support the VoIP application, acting as a gateway to other networks (for example conventional land line networks) where a correspondent terminal is located with which the communication terminal is communicating. Additionally, if the correspondent terminal is another VoIP terminal in the same packet data network, the VoIP server may provide general control plane functions.
Another example communication service is media data streaming from a media server to a terminal across a packet data network. In this example a terminal may request access to media data such as video data, stored on the media server. In response the media server “streams” media data to the terminal across the packet data network by communicating a stream of successive packets to the terminal. Typically, the terminal will only store a fraction of the total media being streamed (for example in a buffer), decoding and reproducing most of the media in real-time.
Other communications systems are provided which enable devices to move around within a network whilst still accessing services and applications provided by a remote host. An example of such a system provides a packet data network including an internet protocol multimedia sub-system (IMS). Mobile nodes can roam within the packet data network, for example connecting to the network at various wireless connection points, whilst accessing services and applications provided by the IMS.
Although users of communications terminals may enjoy multimedia communication services provided by an IMS, these services require that a packet data network, which provides communication of packet data along the data path, is able to provide a sufficient quality of service to support the multimedia communication services.